Placentia Bay is a body of water on the southeast coast of Newfoundland, Canada. It is formed by Burin Peninsula on the west and Avalon Peninsula on the east. Fishing grounds in the bay were used by native people long before the first European fishermen arrived in the 16th century. For a time, the French controlled the bay. They built their capital at Placentia on the east coast. The British gained Placentia during the Treaty of Utrecht in 1713. The town and nearby Castle Hill are national historic sites.